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Abstract:

A method and nodes for providing adaptive segmentation in a higher
protocol layer interacting with a lower protocol layer. An adaptable
segmentation limit, defining a threshold of a largest Protocol Data Unit
(PDU) that is to be submitted to a lower protocol layer, is deployed at a
higher protocol layer interacting with the lower protocol layer. For each
Service Data Unit (SDU) arriving at the higher protocol layer, it is
determined if the respective SDU can fit into the segmentation limit or
not. Each SDU that do not fit into the segmentation limit is segmented
into PDUs which are smaller than or equal to the segmentation limit,
while no segmentation is performed on SDUs that fit into the segmentation
limit.

Claims:

1. A method of providing adaptive segmentation in a higher protocol layer
interacting with a lower protocol layer, comprising: deploying an
adaptable segmentation limit at the higher protocol layer which defines a
threshold of a largest Protocol Data Unit (PDU) to be submitted to the
lower protocol layer; determining, at the higher protocol layer and for
each arriving Service Data Unit (SDU), if the SDU can fit into the
segmentation limit or not; segmenting, at the higher protocol layer, each
SDU that does not fit into the segmentation limit into PDUs which are
smaller than or equal to the segmentation limit, and performing no
segmentation on each SDU that fits into the segmentation limit; and
submitting the resulting one or more PDUs to the lower protocol layer.

2. The method of claim 1 wherein the segmenting further comprises:
concatenating remaining SDUs into a PDU which fits into the segmentation
limit, after having segmented one or more SDUs; or if no segmentation is
being performed, concatenating two or more SDUs into a PDU until the
segmentation limit is reached.

3. The method of claim 1 wherein the deploying comprises dynamically
adapting the segmentation limit based on an indication signaled from the
lower protocol layer.

4. The method of claim 3 wherein the indication includes a notification
of a PDU size limit defining the largest PDU size which is accepted by
the lower protocol layer.

5. The method of claim 1 wherein the segmentation limit is adjusted based
on an observation of residual loss rate in the higher layer protocol.

6. The method of claim 5 wherein the residual loss rate is monitored
periodically in the higher layer protocol.

7. The method of claim 5: wherein, upon observing that the residual loss
rate is above a predetermined loss rate threshold, the segmentation limit
is adjusted by lowering the segmentation limit by a predetermined
decreasing amount; and wherein, upon observing that the residual loss
rate is below the loss rate threshold, the segmentation limit is adjusted
by increasing the segmentation limit by a predetermined increasing
amount.

8. The method of claim 1 wherein the segmenting comprises segmenting each
SDU to be segmented into one of the following: at least one PDU of the
same size as the segmentation limit; PDUs that match a transport block
size that is available in the lower protocol layer; PDUs that match the
largest transport block size that is available in the lower protocol
layer; PDUs of equal size if perfect division into PDUs of equal size is
possible; PDUs of approximately equal sizes if perfect division into PDUs
of equal size is not possible.

9. The method of claim 1 wherein the higher protocol layer is a Radio
Link Control (RLC) protocol layer.

10. The method of claim 1 wherein the higher protocol layer is located in
a Radio Network Controller (RNC) or in a user equipment.

11. The method of claim 1 wherein the lower protocol layer is a Medium
Access Control (MAC) protocol layer.

12. The method of claim 1 wherein the lower protocol layer is located in
any of a Node B, an RNC, or a user equipment.

13. The method of claim 1 wherein the higher protocol layer and the lower
protocol layer are located in different nodes.

14. A method of adaptively adjusting a segmentation limit, comprising:
defining a threshold of a largest Protocol Data Unit (PDU) that is to be
submitted from a higher layer protocol to a lower protocol layer
interacting with the higher protocol layer, the threshold being used for
deploying adaptive segmentation; wherein the segmentation limit is
dynamically adapted based on an indication signaled from the lower
protocol layer to the higher protocol layer.

15. The method of claim 14 wherein the indication includes a notification
of a PDU size limit, defining a largest PDU size which is accepted by the
lower protocol layer.

16. The method of claim 15 wherein the indication is signaled to the
higher protocol layer periodically.

17. The method of claim 16 wherein the indication further includes a
request to the higher layer protocol to discard a number of SDUs when:
the lower protocol layer has failed to transmit the SDUs due to excessive
SDU size; or it has been estimated by the lower layer protocol that the
SDUs cannot be transmitted successfully within a predetermined time
limit.

18. The method of claim 15 wherein the indication is signaled to the
higher protocol layer when it is found that the PDU size limit has been
changed to a level lower than a predefined updating threshold.

19. The method of claim 15 wherein the indication is signaled to the
higher protocol layer when the PDU size limit has been changed by a
configurable amount.

20. The method of claim 15 wherein the indication is signaled to the
higher protocol layer when the lower protocol layer receives an SDU from
the higher protocol layer which was too large to be successfully
delivered to a receiving peer by the lower protocol layer.

21. The method of claim 15 wherein the indication further includes a
request to the higher protocol layer to re-segment a number of SDUs into
a smaller PDU size where: each PDU that is required to be re-segmented by
the higher protocol layer is explicitly indicated; or a reference
indicating which sequence number and forward re-segmentation is required.

22. The method of claim 15 wherein the PDU size limit is updated in the
lower protocol layer based on at least one of the following parameters: a
largest unblocked transport block; a largest available transport block; a
link quality; available scheduling grants; available resources.

23. The method of claim 22 wherein the available resources comprise any
of the following resources: transmission power; frequency resources; time
slots.

24. The method of claim 22 wherein the at least one parameter is
monitored periodically in the lower protocol layer.

25. The method of claim 24 wherein upon observing that the value of the
parameter is above a predetermined quality threshold, the PDU size limit
is set to a predetermined, maximum size.

26. The method of claim 25 wherein the PDU size limit is signaled to the
higher protocol layer when it has been set.

27. A node in a communication network, the node being operative to
provide adaptive segmentation in a higher protocol layer interacting with
a lower protocol layer, the node configured to: deploy an adaptable
segmentation limit at the higher protocol layer that defines a threshold
of a largest PDU to be submitted to a lower protocol layer; receive one
or more SDUs in the higher protocol layer; determine, for each SDU, if
the SDU can fit into the segmentation limit or not; segment an SDU that
does not fit into the segmentation limit into PDUs which are smaller than
or equal to the segmentation limit, and perform no segmentation on an SDU
that fits into the segmentation limit; and submit the resulting one or
more PDUs to the lower protocol layer.

28. The node of claim 27 wherein the node is configured to segment the
SDU by being configured to: concatenate remaining SDUs into a PDU, which
fits into the segmentation limit, after having segmented one or more
SDUs; or if no segmentation is being performed, concatenate two or more
SDUs into a PDU until the segmentation limit is reached.

29. The node of claim 27 wherein the node is further configured to change
the segmentation limit with a configurable amount based on an indication
signaled from the lower protocol layer.

30. The node of claim 29 wherein the indication includes a notification
of a PDU size limit, defining the largest PDU size which is accepted by
the lower protocol layer.

31. The node of claim 27 wherein the node is configured to segment an SDU
into one of the following: at least one PDU of the same size as the
segmentation limit; PDUs that match a transport block size that is
available in the lower protocol layer; PDUs that match a largest
transport block size that is available in the lower protocol layer; PDUs
of equal size if perfect division into PDUs of equal size is possible; or
PDUs of approximately equal sizes if perfect division into PDUs of equal
size is not possible.

32. The node of claim 27 wherein the node is further configured to
adaptively adjust the segmentation limit based on an observation of
residual loss rate in the higher protocol layer.

33. The node of claim 32 wherein the node is further configured to
monitor the residual loss rate periodically.

34. The node of claim 32 wherein the node is configured to adjust the
segmentation limit by being configured to: lower the segmentation limit
by a predetermined decreasing amount if the residual loss rate is found
to be above a predetermined loss rate threshold; and increase the
segmentation limit by a predetermined increasing amount if the residual
loss rate is found to be below the loss rate threshold.

35. The node of claim 27 wherein the higher protocol layer is a Radio
Link Control (RLC) protocol layer.

36. The node of claim 27 wherein the node is any of a Radio Network
Controller (RNC), a Node B or a user equipment.

37. The node of claim 27 wherein the lower protocol layer is a Medium
Access Control (MAC) protocol layer.

38. A node in a communication network operative to provide adaptive
segmentation in a higher protocol layer interacting with a lower protocol
layer of the node, the node configured to: adjust a PDU size limit
defining the largest PDU size which is accepted by the lower protocol
layer; signal an indication including a notification of the PDU size
limit to the higher protocol layer, to be used when adaptively adjusting
a segmentation limit, the indication defining a threshold of a largest
PDU that is submitted to the lower protocol layer; receive one or more
PDUs submitted from the higher protocol layer.

39. The node of claim 38 wherein the node is configured to update the PDU
size limit periodically.

40. The node of claim 38 wherein the node is configured to signal the
indication periodically.

41. The node of claim 38 wherein the node is configured to signal the
indication when the PDU size limit is changed by a configurable amount,
in order to reduce the amount of indication messages.

42. The node of claim 38 wherein the node is configured to signal the
indication when the lower protocol layer has received an SDU from the
higher protocol layer which was too large to be successfully delivered to
a receiving peer by the lower protocol layer.

43. The node of claim 39 wherein the node is configured to determine
which PDUs have been transmitted successfully, and include a request in
the indication to the higher protocol layer to discard a number of SDUs
when: it has been determined that the lower protocol layer has failed to
transmit the SDUs due to excessive SDU size; or it has been estimated
that the SDUs cannot be transmitted successfully within a predetermined
time limit.

44. The node of claim 39 wherein the node is configured to update the PDU
size limit based on at least one of the following parameters: a largest
unblocked transport block; a largest available transport block; a link
quality; available scheduling grants; available resources.

45. The node of claim 44 wherein the available resources comprise any of
the following resources: transmission power; frequency resources; time
slots.

46. The node of claim 44 wherein the node is configured to monitor the at
least one parameter periodically.

47. The node of claim 44 wherein the node is configured to set the PDU
size limit to a predetermined, maximum size if it is determined that the
parameter is above a predetermined quality threshold.

48. The node of claim 47 wherein the node is configured to signal the PDU
size limit to the higher protocol layer when it has been updated.

49. The node of claim 38 wherein the node is a Node B or a user
equipment.

50. The node of claim 38 wherein the higher protocol layer is the Radio
Link Control (RLC) protocol layer.

51. The node of claim 38 wherein the lower protocol layer is the Medium
Access Control (MAC) protocol layer.

Description:

[0001] This application is a continuation of U.S. patent application Ser.
No. 12/278,649, filed Aug. 7, 2008, which is a national stage application
of PCT/SE2007/050061, filed Feb. 5, 2007, and claims benefit of U.S.
Provisional Application 60/743,241, filed Feb. 7, 2006, the disclosures
of each of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

[0002] The present invention relates generally to the field of
segmentation and concatenation of Service Data Units (SDUs) into Protocol
Data Units (PDUs) in a higher protocol layer, and more particularly of
reducing the overhead due to segmentation and/or concatenation.

BACKGROUND

[0003] In the Universal Mobile Telecommunications System (UMTS) a general
protocol reference model containing a layered protocol stack is used for
providing reliable communication of user data and signalling between the
nodes of the network. UMTS also employs the concept of control-plane and
user-plane, where the control-plane is a set of protocols used
exclusively for control signalling purposes, while the user-plane is used
exclusively for user data transfer.

[0004] A user-plane protocol stack in UTRAN according to the prior art is
illustrated in FIG. 1. The figure illustrates the protocol stack of a
User Equipment (UE) 100 communicating with a Serving Radio network
Controller (SRNC) 110 and an intermediate Node B 120. The Physical layer
(PHY) 101,121 offers services to the Medium Access (MAC) layers via
transport channels, while the MAC layers (MAC_e/hs/d) 102,103,111,122, in
turn, offers services to the Radio Link Control (RLC) layer 104,112 by
means of logical channels. MAC-d handles dedicated channels, which may be
mapped to common transport channels, wherein MAC-d passes data to MAC-hs
or MAC-e. MAC-hs denotes the downlink MAC entity and is used for serving
the High Speed Downlink Shared Channel (HS-DSCH), introduced in Release 5
of the 3GPP specification, while MAC-e denotes a MAC entity related to
the new uplink channel, Enhanced Dedicated Channel (E-DCH), introduced in
Release 6.

[0005] In the user-plane, which is illustrated by the figure, the RLC
layer offers services to the Packet Data Convergence Protocol (PDCP)
105,113. A control-plane may be illustrated by simply changing the PDCP
layer to a Radio Resource Control (RRC) layer.

[0006] A Service Data Unit (SDU) can be conceptualized as a data unit
received from, or submitted to, a higher protocol layer, e.g. RLC. A
Protocol Data Unit (PDU) is a unit which is submitted to, or received
from, a protocol layer logically located beneath the protocol from which
the SDU is received. The PDU comprises a mandatory header and, optionally
also a Length Indicator (LI), which indicates the last octet of each
higher-layer SDU, ending within the PDU. The PDU also comprises a data
field, containing one or more segments from one or more higher-layer
PDUs.

[0007] The RLC protocol provides radio bearers for user data transfer and
signalling radio bearers for control signalling and includes
functionality such as RLC segmentation, re-assembly, and potentially also
concatenation of RLC SDUs into RLC PDUs. At the transmitting end,
segmentation and/or concatenation is used in order to match currently
used Transport Formats (TF), i.e. predetermined PDU sizes. In the
receiving end the segments belonging to one higher-layer PDU are
re-assembled before they are delivered to the higher-layer. An RLC SDU is
typically an IP Packet or a signalling message, while an RLC PDU
typically is a MAC_d SDU. If a higher-layer PDU segment does not
completely fill the payload field of the RLC PDU, the first segment in
the next higher-layer PDU may be put in the RLC PDU in concatenation with
the last segments of the previous higher-layer PDU.

[0008] The RLC protocol includes the three different modes Transparent
Mode (TM), Unacknowledged Mode (UM) and Acknowledged Mode (AM). In AM,
the RLC deploys re-transmission to guarantee lossless delivery of all RLC
PDUs, while no re-transmission, and, hence, no guarantee of data delivery
is deployed in UM. In TM, no protocol overhead is added by the RLC layer.
The present invention is applicable to the UM and AM modes.

[0009] Both UM and AM of RLC uses segmentation and optionally
concatenation on the transmitter side, while re-assembly is used on the
receiver side.

[0010] In the current UTRAN architecture, the RLC protocol is terminated
in the Serving Radio Network Controller (SRNC) and in the User Equipment
(UE), respectively. The present invention does, however, not preclude a
different architecture, where the terminating point of the protocol
deploying segmentation, re-assembly and concatenation is placed
elsewhere, e.g. in the base station (node B). The RLC PDUs are submitted
to, and received from, the Medium Access Control (MAC) protocol, which
realizes the transport channels over the UMTS air-interface, the Uu
interface.

[0011] In the existing UTRAN protocol stack, the RLC PDU size for a given
radio bearer can only take a discrete number of different sizes, which
are configurable by upper layers of the protocol stack. For RLC AM, the
RLC PDU size can only take a single value. The most commonly used RLC PDU
size for user-plane transmissions is 320 bits of payload and a 16 bits
RLC header. It can be configured and re-configured by higher-layers, and
bearers carrying signalling typically deploy a PDU size, carrying 128
bits of payload.

[0012] For RLC UM, there is a possibility to configure several RLC PCU
sizes. The header fields in MAC-hs and MAC-e, however, restrict the
de-facto numbers of different sizes that can be used. For example, it is
currently possible to use maximally eight different MAC-d PDU sizes over
HS-DSCH, where a MAC-d PDU is an RLC PDU and an optional MAC-d header.

[0013] The fact that the RLC PDU size can only take one single size, or a
discrete set of sizes, means that RLC SDUs typically need to be segmented
and/or concatenated into an appropriate number of RLC PDUs. One drawback
with such a limitation can be extensive protocol overhead and padding.
Padding occurs if concatenation cannot be used, i.e. the remaining
payload to be segmented into an RLC PDU does not fill the available space
of the most suitable RLC PDU size. Such a situation can be illustrated
with the two following examples.

[0014] In a first example we consider the transmission of one 1500 octet
IP packet. It is assumed that an RLC PDU size of 320 bits, i.e. 40
octets, is used for segmentation. This implies that the IP packet is
segmented into 38 RLC PDUs, having the capacity of delivering 1520
octets.

[0015] In this case, the RLC header overhead equals 38*2 octets and a one
octet length indicator, inserted in the last RLC PDU, which makes a total
of 77 octets, while padding, which is used to fill up the last RLC PDU,
equals 19 octets. This means that for the transmission of 1500 octets, a
total RLC overhead of 96 octets will be necessary.

[0016] In a second example, the transmission of one compressed Transport
Communication Protocol Acknowledgement (TCP ACK) is considered. A TCP ACK
is typically 40 bytes long. In this example it is assumed that a TCP ACK
is compressed down to four octets by a conventional header compression
protocol. The RLC protocol adds a two octet fixed header and a one octet
length indicator and adds padding up to the full RLC PDU size. With the
typical RLC PDU size of 320 bits, this implies a 38 octet header overhead
and padding for transmission of just four octets of payload.

[0017] The first example clearly illustrates the deficiency of using fixed
RLC PDUs when segmenting and/or concatenating large RLC SDUs, while the
second example shows the inefficiency which may occur when segmenting
and/or concatenating small RLC SDUs.

[0018] To overcome the problems mentioned above, an RLC protocol that is
able to use any RLC PDU size has been proposed in R2-052508 "User plane
protocol enhancements", presented at TSG-RAN WG2 Meeting
#48bis,Cannes,France, 10-14 Oct. 2005. Such a flexible RLC solution may
allow arbitrary RLC PDU sizes, such that the RLC PDU equals the size of
the RLC SDU and the necessary RLC header, and may also provide a minimal
level of RLC overhead. In addition, such a solution may remove the need
for padding. In the first example, mentioned above, the required overhead
with the solution proposed in R2-052508 "User plane protocol
enhancements", would be 2 octets, as opposed to 96 octets. In both
examples, the padding would be zero octets, as opposed to 19 and 38 in
the first and second example, respectively.

[0019] Still, a problem of handling large RLC SDUs, i.e. large IP packets
or long signalling messages may occur also when using the solution
referred to in R2-052508, especially when transmission coverage and RLC
AM re-transmission efficiency is considered.

[0020] This deficiency can be illustrated in a first scenario, wherein a
large SDU PDU of 1500 octets is forwarded to the MAC protocol as a single
RLC PDU, without deploying any segmentation. The transmission of the RLC
PDU in a single transport block in MAC-hs or in MAC-e may lead to
coverage problems, i.e. a sufficiently large transport block may not be
supported in the whole cell, which may result in a failure to deliver the
large RLC PDU. In other words, if the link quality between a user
equipment and a radio base-station is bad, the MAC protocol may fail to
deliver such a large block as a single transmission unit. Trying to solve
the scenario described above by adapting the transmission blocks size to
the link-quality by introducing segmentation and concatenation into MAC,
may not be adequate, since such a solution may result in a low RLC AM
re-transmission efficiency. Considering once again the first example,
described above, assuming that MAC-hs segments the IP- packet into 38
transport blocks. Hybrid Automatic Repeat Request (HARQ) is an advanced
retransmission strategy, which allows the performing of possible
re-transmissions directly at the physical/MAC layer. This is done without
involving higher-layer mechanisms and so reduces the delay.

[0021] Due to an error in the HARQ feedback signalling or an error caused
by the reaching of the maximum number of HARQ re-transmissions, all but
one of the respective transmission blocks may be successfully delivered.
In such a case, the whole RLC PDU of a 1500 octet and an RLC header has
to be re-transmitted, resulting in a very low RLC re-transmission
efficiency.

[0022] Despite the obvious performance benefits gained from using a
flexible RLC according to the prior art, the scenario described above
clearly illustrates that there are situations when large RLC PDUs can
create problems, which typically occur at times of bad link quality, or
when there are not enough of transmission resources in terms of power,
spectrum or time-slots available.

SUMMARY

[0023] The object of the present invention is to address at least some of
the problems outlined above. More specifically, the present invention
solves the aforementioned problems by providing and implementing an
adaptive segmentation limit according to the independent claims described
below.

[0024] An adaptable segmentation limit, defining a threshold of a largest
Protocol Data Unit (PDU) that is submitted to a lower protocol layer, is
deployed at a higher protocol layer interacting with the lower protocol
layer. For each Service Data Unit (SDU) arriving at the higher protocol
layer, it is determined if the respective SDU can fit into the
segmentation limit or not. Each SDU that do not fit into the segmentation
limit is segmented into PDUs which are smaller than or equal to the
segmentation limit, while no segmentation is performed on SDUs that fit
into the segmentation limit. The resulting PDU or PDUs are then submitted
to the lower protocol layer.

[0025] SDUs that remain after a segmentation or when no segmentation is
found necessary may be concatenated if concatenation is supported.

[0026] The suggested adaptive segmentation may be executed using any of a
number of alternative conditions, either alone or in a combination. One
or more PDUs may be set to the same size as the segmentation limit. PDUs
may match either the largest, or any transport block size that is
available in the lower protocol layer. PDUs may also be set to equal size
if perfect division into PDUs of equal size is possible, or to
approximately equal size if perfect division is not possible.

[0027] The segmentation limit may be dynamically adapted on the basis of
an indication, signalled from the lower protocol layer, including a
notification, denoted the PDU size limit, of the largest PDU size which
is accepted by the lower protocol layer. The indication may be updated
and signalled to the higher protocol layer according to one or more
alternative conditions. A change of the PDU size limit to a level, lower
than a predefined updating threshold may define one way of triggering
signalling of an indication. Unsuccessful delivering of PDUs from the
lower protocol layer to a receiving peer may also trigger signalling of
an indication from the lower protocol layer to the higher protocol layer.
The indication may also include a request for re-segmentation or to
discard one or more SDUs.

[0028] The PDU size limit may be updated periodically or on the basis of
one or more monitored parameters, such as available or unblocked
transport blocks, link quality, available scheduling grants or available
resources.

[0029] Alternatively, or in a combination, the segmentation limit may be
adjusted on the basis of the residual loss-rate, observed in the higher
protocol layer. After having compared the observed loss-rate to a
loss-rate threshold, the segmentation limit is adjusted by a
predetermined amount. The observation may be executed periodically or
according to any other predetermined condition.

[0030] Under favourable conditions, such as, e.g. high link quality, the
proposed adaptive segmentation may be considered superfluous. Under those
circumstances the PDU limit may be set to a predetermined, relatively
large size, which is signalled to the higher protocol layer. Since all
SDUs will now fit into the segmentation limit, segmentation will be
cancelled until the segmentation limit is updated with a lower value.

[0031] A node is adapted to provide adaptive segmentation in a higher
protocol layer interacting with a lower protocol layer which comprises:
means for deploying an adaptable segmentation limit the higher protocol
layer, defining a threshold of the largest PDU to be submitted to a lower
protocol layer; means for receiving one or more SDUs by the higher
protocol layer; means for determining for each SDU if the SDU can fit
into the segmentation limit or not; means for segmenting an SDU that do
not fit into the segmentation limit, into PDUs which are smaller than or
equal to the segmentation limit, or performing no segmentation on an SDU
that fit into the segmentation limit, and; means for submitting the
resulting PDU/PDUs to the lower protocol layer. The segmenting means of
the node may be adapted to perform concatenation according to the
following rules:

[0032] concatenating remaining SDUs into a PDU, which fit into the
segmentation limit, after having segmented one or more SDUs, or, in case
no segmentation is being performed; concatenating two or more SDUs into a
PDU until the segmentation limit is reached.

[0033] Another node to be used in a communication network, providing
adaptive segmentation in a higher protocol layer interacting with a lower
protocol layer of said node comprises the following means: means for
adjusting a PDU size limit, defining the largest PDU size which is
accepted by the lower protocol layer; means for signalling an indication,
including a notification of the PDU size limit to the higher protocol
layer, to be used when adaptively adjusting a segmentation limit,
defining a threshold of a largest PDU that is submitted to the lower
protocol layer; means for receiving one or more PDUs, submitted from said
higher protocol layer.

[0034] The higher protocol layer may be e.g. the RLC protocol layer, and
the protocol may be locate in a node such as e.g. an RNC, node B or a
user equipment. The lower protocol layer may be e.g. the MAC protocol
layer, which may be located in another node, e.g. a node B or a user
equipment, interacting with the node comprising the higher protocol
layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will now be described in more detail by means
of exemplary embodiments and with reference to the accompanying drawings,
in which:

[0036] FIG. 1 is a basic overview of a procedure, according to the prior
art.

[0037] FIG. 2a is an illustration of an evaluation situation where an SDU
is smaller than a specified segmentation limit, in accordance with one
embodiment.

[0038] FIG. 2b is an illustration of another situation in which an SDU is
larger than a specified segmentation limit, in accordance with another
embodiment.

[0039] FIG. 3 is a flow chart illustrating a basic procedure for deploying
a segmentation limit in accordance with another embodiment.

[0040]FIG. 4a is a flow chart illustrating a procedure for adaptively
adjusting a segmentation limit in a higher protocol layer in accordance
with another embodiment.

[0041]FIG. 4b is a flow chart illustrating an alternative procedure for
adaptively adjusting a segmentation limit in an higher protocol layer in
accordance with yet another embodiment.

[0042] FIG. 5a is a flow chart illustrating a procedure for adjusting a
PDU size limit in a lower protocol layer in accordance with another
embodiment.

[0043]FIG. 5b is a flow chart illustrating a procedure for adjusting a
PDU size limit in a lower protocol layer in accordance with yet another
embodiment.

[0044]FIG. 6 is a schematic illustration of a node, having a higher
protocol layer, responsible for performing adaptive segmentation and/or
concatenation, in accordance with another embodiment.

[0045]FIG. 7 is a schematic illustration of a node having a lower
protocol layer, adapted to receive adaptively segmented and/or
concatenated PDUs from a higher protocol layer, according to another
embodiment.

DETAILED DESCRIPTION

[0046] Briefly described, the present invention provides a method and
nodes in a communication network which are adapted for providing adaptive
segmentation and concatenation.

[0047] According to the claimed invention, adaptive segmentation and/or
concatenation is provided by way of introducing an adaptively adjustable
segmentation limit to be deployed in a higher protocol layer, which is
responsible for segmentation and/or concatenation. The higher protocol
layer in question may be located in any type of node, adapted to perform
segmentation and/or concatenation, such as, e.g. an RNC, a node B or a
user equipment. The segmentation limit according to the claimed invention
defines a threshold of the largest PDU that is to be submitted to a lower
protocol layer by a higher protocol layer sender, deploying segmentation
and/or concatenation. The lower protocol layer may be located in, e.g. a
node B, a user equipment or any other node to which one or more PDUs are
submitted from a higher protocol layer.

[0048] FIG. 2a shows one possible scenario in which a segmentation limit
200 has been deployed. The SDU 201 is found to fit into an approved PDU
format, i.e. the size of the resulting PDU does not exceed the largest
acceptable PDU size, denoted the PDU size limit. When this condition is
met, a header will be attached to the SDU, and the resulting PDU 202,
will be submitted from the protocol sender to a lower protocol layer,
without performing any segmentation or concatenation in the higher
protocol layer. In the scenario described by FIG. 2b, however, the size
of the SDU 203 is found to be too large to fit into one PDU of acceptable
size, i.e. the SDU is larger than the segmentation limit 204. In this
case, the SDU needs to be segmented, such that the sizes of each
resulting PDU 205 and 206 is less than or equal to the segmentation
limit. In the figure, the first PDU, PDU1, equals the size of the
segmentation limit, while the size of the second PDU, PDU 2 is smaller
than the segmentation limit.

[0049] One embodiment for using the proposed segmentation limit according
to one embodiment will now be described with reference to FIG. 3.

[0050] FIG. 3 illustrates one way of providing adaptive segmentation
and/or concatenation by way of using a segmentation limit, starting at
step 300. At a next step 301, the adaptively adjustable segmentation
limit is deployed in a higher protocol layer responsible for performing
segmentation and/or concatenation. Initially the segmentation limit is
set to a starting value, according to one or more predetermined
conditions. Alternative embodiments for adjusting the segmentation limit
will be described below with reference to FIGS. 4a and 4b.

[0051] Arriving SDUs, illustrated by step 302, to be submitted from a
higher protocol layer to a lower protocol layer as one or more PDUs, are
compared to the segmentation limit in a next step 303, where it is
determined whether an SDU will fit into the segmentation limit or not. If
the SDU is found not to fit into the segmentation limit, the SDU is
segmented into PDUs which are smaller than or equal to the segmentation
limit in step 304, before the resulting PDUs are submitted to a lower
protocol layer in step 305. If, however, an SDU is found to fit into the
segmentation limit, the resulting PDU is submitted without performing any
segmentation. The described procedure is repeated for each arriving SDU
as long as the segmentation limit is deployed by the system. If
supported, the SDUs may be concatenated, either in combination with
segmentation or without using segmentation. SDUs which remain after a
segmentation may be concatenated into a PDU, which fit into the
segmentation limit. If no segmentation is being performed, two or more
SDUs may be concatenated into a PDU until the segmentation limit is
reached and no more SDU will fit into the PDU.

[0052] The segmentation which is performed in step 304 may be done
according to one or more predefined rules, some of which will now be
described.

[0053] According to a first embodiment, an SDU is segmented and/or
concatenated into PDUs in such a way that the size of at least one PDU is
equal to the segmentation limit. In another embodiment, an SDU is
segmented and/or concatenated into equally sized PDUs which fit into the
segmentation limit. If, however, no division into equally sized PDUs is
possible, the respective SDU may instead be segmented and/or concatenated
into PDUs of approximately equal size. In yet another embodiment, an SDU
may be segmented and/or concatenated into PDUs which match any available
transport block sizes in MAC, or, alternatively, the largest available
transport block.

[0054] In FIG. 4a one embodiment for adjusting the segmentation limit is
described. The procedure, starting in step 400, is being executed in the
higher protocol layer which is responsible for segmentation and/or
concatenation. One way of providing adjustment of the segmentation limit
is to indicate the largest PDU size to be accepted by a lower protocol
layer, to which one or more PDUs are to be submitted. This indication
will include a notification of the largest acceptable PDU size, hereby
defined as the PDU size limit. The PDU size limit is adjusted in the
lower protocol layer according to predetermined adjusting conditions and
is also signalled to the higher protocol layer according to predetermined
signalling conditions. In FIG. 4a, a check for a new indication,
comprising the proposed PDU size limit, is executed in step 401. Such a
checking procedure may be executed periodically or according to one or
more alternative conditions. When an indication is received at the higher
protocol layer, the segmentation limit is adjusted, taking the received
PDU size limit into consideration. The adjustment, which is execute in
step 402, is done according to one or more predetermined conditions.

[0055] An alternative way of adjusting the segmentation limit will now be
describe with reference to FIG. 4b. This alternative embodiment, which
starts at step 403, refers to an updating procedure which is executed in
the higher protocol layer, responsible for segmentation and
concatenation. An observed residual loss-rate, which may be monitored
periodically, is compared to an upper loss-rate threshold in step 404. If
the loss-rate is found to be higher than the upper loss-rate threshold,
the segmentation limit is decreased with a pre-determined amount in step
405.

[0056] In a next step 406 the loss rate is compared to a lower loss-rate
threshold. If the residual loss-rate is found to be below the lower
loss-rate threshold, the segmentation limit is instead increased with a
pre-determined amount in step 407. It is to be understood that the two
alternative embodiments described with reference to FIGS. 4a and 4b may
be implemented separately or in a combination.

[0057] One embodiment for adjusting a PDU size limit in a lower protocol
layer and for signalling the PDU size limit to the respective higher
protocol layer will now be described with reference to FIG. 5a. The
procedure, starting in step 500, may be executed periodically as long as
a segmentation limit according to the claimed invention is deployed. In
step 501 it is determined if a predetermined condition for adjusting the
PDU size limit has been triggered. Upon detecting that a condition for
adjusting the PDU size limit has occurred, the PDU size limit is adjusted
according to a predetermined rule. In a next step 503 it is determined if
a predetermined condition for signalling the PDU size limit to a
respective upper-layer protocol has occurred. If a signalling is
triggered, the recently updated PDU size limit is signalled to the
respective higher protocol layer in a final step 504, where the
indication, comprising the PDU size limit will trigger an adjusting
procedure, adapted to adjust the segmentation limit, as described above.

[0058] The conditions for adjusting the PDU size limit may be defined
according to different preferred criteria. According to one embodiment, a
parameter, such as largest unblocked transport block, largest available
transport block, link quality, available scheduling grants or available
resources may be monitored periodically, or according to any other
predetermined rule. Available resources may comprise resources such as
transmission power, frequency resources or time-slots. FIG. 5b
illustrates a way of triggering an adjustment which has the purpose of
cancelling the segmentation limit when a quality parameter, which is
monitored in the lower protocol layer, indicates such a high quality that
the use of a flexible segmentation is found superfluous. Such a
monitoring is done in step 506 in the figure. In step 507, PDU size limit
is set to a predefined, high value, hereby denoted maximum size.

[0059] By setting PDU size limit to maximum limit, the segmentation limit
will be adjusted to a value high enough to allow all possible SDUs to fit
into the segmentation limit. Since all SDUs will now fit into the
segmentation limit, segmentation practically will be cancelled until the
segmentation limit is updated with a lower value.

[0060] Also the conditions for triggering the signalling of the latest
updated PDU size limit may be set according to different preferences.
According to one embodiment, indications are configured to be signalled
on a periodical basis. In another embodiment an indication is configured
to be signalled when PDU size limit is found to be lower than a
pre-defined updating threshold. In yet another embodiment an indication
is instead signalled when it is found that PDU size limit has been
changed above a certain configurable amount, in order to reduce the
amount of indication messages, sent from the lower protocol layer to the
respective higher protocol layer. The proposed alternative adjustment
trigger conditions, as well as the alternative signalling trigger
conditions mentioned above, may be implemented alone or in any
alternative combination.

[0061] The proposed indication may be used also for forwarding additional
instructions in connection with the proposed adjusting procedure.
According to one embodiment, the indication also includes a request for
re-segmentation from the respective higher protocol layer. Such a request
may comprise an explicit indication of all PDUs to be re-segmented.
Alternatively, a request may comprise the last successfully transmitted
PDU. Such a request may result in that all subsequent PDUs are
re-segmented by the respective higher protocol layer. In yet another
embodiment the indication may comprise a request to the respective higher
protocol layer to discard a number of SDUs, when it is found that the
lower protocol layer has failed to transmit the respective SDUs, due to
excessive size. Another condition for requesting for discarding of SDUs
may be if it has been estimated that a number of SDUs can not be
successfully transmitted within a predetermined time-limit.

[0062] The functionality in a node suitable for performing segmentation
and/or concatenation according to one embodiment will now be
schematically described with reference to FIG. 6. It is to be noted that
this node 600 could be any type of communication node which is adapted to
perform segmentation and/or concatenation. An SDU received in a receiving
means 601 is forwarded to a determining means 602 for determining whether
segmentation and/or concatenation is to be executed. The determining
means comprises means for deploying a segmentation limit according to any
of the embodiments proposed above, and means for determining if a
received SDU fit into the segmentation limit or not. Next, the SDU is
passed to a segmentation and concatenation means 603, where the SDU is
segmented and/or concatenated according to any of the embodiments
proposed above if the SDU if found not to fit into the segmentation limit
by the determining means. The resulting PDUs are then submitted to a
respective lower protocol layer by a submitting means 604. If, however,
the SDU if found to fit into the segmentation limit, the resulting on or
more PDUs are submitted to a respective lower protocol layer by the
submitting means according to conventional procedures.

[0063] According to the different proposed embodiments of the claimed
invention, a PDU size limit is updated and signalled in a lower protocol
layer, adapted to receive PDUs, submitted from a higher protocol layer.
FIG. 7 schematically illustrates the functionality necessary for
providing such a service to the higher protocol layer. The node 700
comprises an adjusting means adapted to adjust a PDU size limit when an
adjustment trigger has been activated. The latest updated PDU size limit
is signalled to the respective higher protocol layer from a signalling
means 702 when a signalling trigger has been activated. The signalling
means also may comprise means adapted to determine which PDUs that have
been successfully transmitted, and means adapted to include a request to
discard a number of SDUs, when it has been determined that transmitting
of these SDUs has failed due to excessive size.

[0064] This means also may be adapted to use an estimating scheme for
estimating whether a number of SDUs can be transmitted successfully
within a predetermined time-limit or not. Also the result from this
estimation may be used for requesting for a number of SDUs to be
discarded in the higher protocol layer.

[0065] While the invention has been described with reference to specific
exemplary embodiments, the description is generally only intended to
illustrate the inventive concept and should not be taken as limiting the
scope of the invention, which is defined by the appended claims.

Patent applications by Johan Torsner, Masaby FI

Patent applications by TELEFONAKTIEBOLAGET L M ERICSSON (PUBL)

Patent applications in class Having a plurality of contiguous regions served by respective fixed stations

Patent applications in all subclasses Having a plurality of contiguous regions served by respective fixed stations